Download No Slide Title

IP Addressing & Routing
By
Lal Paul
Systems Administrator
CIRM, CUSAT
Linux Networking
1
Lal Paul
The Internet Protocol (IP)


Provides delivery of packets from one host in the
Internet to any other host in the Internet, even if the
hosts are on different networks
Internet packets are called “datagrams” and may be up
to 64 kilobytes in length (although they are typically
much smaller)
Linux Networking
2
Lal Paul
IP Addresses


32 bits long
Notation:
 Each byte is written in decimal in MSB order,
separated by decimals
 01101001.11111110.00010001.00000001
( 105.254.17.1 – in decimal notation)
Linux Networking
3
Lal Paul
IP Address Classes

Address Classes
 Class A, B, C, D, E
 Loopback
 Broadcast
Linux Networking
4
Lal Paul
IP Address Classes
Class
32 bits
A
0
B
10
C
110
D
1110
E
11110
Linux Networking
Net
Type of Serv.
Host
Net
Host
Net
Host
Multicast address
Reserved
5
Lal Paul
IP Address Classes



Class A:
 For very large organizations
 16 million hosts allowed : from 0xxx, or 1 to 126 decimal.
Class B:
 For large organizations
 65 thousand hosts allowed : from 10xx, or 128 to 191 decimal.
Class C
 For small organizations
 255 hosts allowed : from 110x, or 192 to 223 decimal
Linux Networking
6
Lal Paul
IP Address Classes (Cont’d)
•Class D
Multicast addresses

No network/host hierarchy : 1110, or 224 to 239 decimal.

•Class E
Future Use

begin with 1111, or 240 to 254 decimal.

Linux Networking
7
Lal Paul
Subnets

Large Network
Internet
Linux Networking
8
Lal Paul
Subnets

Departments after subnetting
B
A
192.168.1.0
C
192.168.2.0
192.168.4.0
192.168.3.0
D
Linux Networking
9
Lal Paul
Subnet Masks

A binary number used to compare the destination
address to the local IP address and to determine
whether those destinations are on the same subnet or
not.
Linux Networking
10
Lal Paul
Linux Networking
11
Lal Paul
Linux Networking
12
Lal Paul
Subnet Masks


Assume your machine is 192.168.1.1 and has a subnet
mask 255.255.255.0 and a packet is send to
192.168.1.2
How to find whether the destination host is on the same
subnet or not
 Anding the IP Address with the subnet mask will give
the Network Address.Hence the both Ips are Anded
and the system will determine the network address
Linux Networking
13
Lal Paul
192.168.3.1
255.255.255.0
Net id
192.168.2.0
192.168.2.1
255.255.255.0
Net id
192.168.2.0
192.168.3.1
&&
255.255.255.0
=
192.168.3.0
(Net id)
Hence Accept
192.168.3.1
&&
255.255.255.0
=
192.168.3.0
(Net id)
Hence reject
Linux Networking
14
192.168.1.1
255.255.255.0
Net id
192.168.2.0
Ping 192.168.3.1
Lal Paul
2.3 IP Routing
How do you get a packet
from one network to another?
?
A
Linux Networking
B
C
D
W
15
X
Y
Z
Lal Paul
IP Routing
(cont’d)
Answer: with a router (or a
series of routers)
Case 1:
Single hop
R
A
B
C
D
Case 2:
Multi-hop
Network
Cloud
R
A
Linux Networking
W
B
C
D
X
Y
Z
R
W
16
X
Y
Z
Lal Paul
Example
R1
N1
R2
R3
N2
N3
N4
Dest Next hop
N1
N2
N3
N4
Routing table @ R2
R1
Deliver directly
Deliver directly
R3
Actual routing table contains IP addresses, Flags
indicating type of entries, net mask etc. (see Stevens pg.
113, sect 9.2)
Linux Networking
17
Lal Paul
How packet travels
192.168.1.1
192.168.1.0
255.255.255.0
192.168.1.2
255.255.255.0
Gw:192.168.1.1
10.0.0.1
192.168.2.1
No route
Packet10.0.0.2
send back
10.0.0.3
192.168.2.2
255.255.255.0
Gw:192.168.2.1
192.168.2.0
255.255.255.0
192.168.2.3
255.255.255.0
Gw:192.168.2.1
ping 192.168.3.2
192.168.3.1
192.168.3.2
255.255.255.0
Gw:192.168.3.1
Linux Networking
192.168.3.0
255.255.255.0
192.168.3.2
&&
255.255.255.0
=
192.168.3.0
Packet sent to Gateway
18
Lal Paul
Routing
Routing table
192.168.2.0 --> 10.0.0.2
192.168.3.0 --> 10.0.0.3
192.168.1.1
192.168.2.1
192.168.2.0
255.255.255.0
192.168.1.0
255.255.255.0
192.168.1.2
255.255.255.0
Gw:192.168.1.1
192.168.2.2
255.255.255.0
Gw:192.168.2.1
10.0.0.1
10.0.0.2
10.0.0.3
192.168.2.3
255.255.255.0
Gw:192.168.2.1
ping 192.168.3.2
Routing table
192.168.1.0 --> 10.0.0.1
192.168.3.0 --> 10.0.0.3
192.168.3.2
255.255.255.0
Gw:192.168.3.1
Linux Networking
192.168.3.1
192.168.3.0
255.255.255.0
19
192.168.3.2 && 255.255.255.0
=192.168.3.0
Packet sent to Gateway
Routing table
192.168.1.0 --> 10.0.0.1
192.168.2.0 --> 10.0.0.2
Lal Paul
Ping





Uses ICMP echo request/reply
Source sends ICMP echo request message to the destination
address
 Echo request packet contains sequence number and timestamp
Destination replies with an ICMP echo reply message containing
the data in the original echo request message
Source can calculate round trip time (RTT) of packets
If no echo reply comes back then the destination is unreachable
Linux Networking
20
Lal Paul
Ping (cont’d)
A
R1
R2
R3
B
Echo request
Time
Echo reply
Linux Networking
21
Lal Paul
Traceroute





Traceroute records the route that packets take
A clever use of the TTL field
When a router receives a packet, it decrements TTL
If TTL=0, it sends an ICMP time exceeded message back to the
sender
To determine the route, progressively increase TTL
 Every time an ICMP time exceeded message is received, record
the sender’s (router’s) address
 Repeat until the destination host is reached or an error message
occurs
Linux Networking
22
Lal Paul
Traceroute (cont’d)
Te = Time exceeded
Pu = Port unreachable
A
R1
R2
B
R3
TTL=1, Dest = B,
port = invalid
Te (R1)
TTL=2, Dest = B
Time
Te (R2)
TTL=3, Dest = B
Te (R3)
TTL=4, Dest = B
Pu (B)
Linux Networking
23
Lal Paul
Traceroute Examle
1 lcsr-gw (128.6.13.21) 1.206 ms 0.973 ms 0.782 ms
2 rucs-gw (165.230.212.129) 0.697 ms 0.569 ms 0.571 ms
3 transition2-gw (165.230.12.145) 2.786 ms 0.994 ms 0.769 ms
4 rutgers-gw.Rutgers.EDU (198.151.130.209) 1.726 ms 2.048 ms Vl1000-sr02-hil
l012-svcs.Rutgers.EDU (198.151.130.14) 1.278 ms
5 rutgers-gw.Rutgers.EDU (198.151.130.209) 1.755 ms 1.241 ms 1.828 ms
6 198.151.130.226 (198.151.130.226) 2.748 ms 3.070 ms 2.640 ms
7 clev-nycm.abilene.ucaid.edu (198.32.8.29) 15.162 ms 14.619 ms 14.663 ms
8 ipls-clev.abilene.ucaid.edu (198.32.8.25) 21.220 ms 22.497 ms 21.450 ms
9 kscy-ipls.abilene.ucaid.edu (198.32.8.5) 30.257 ms 30.604 ms 30.969 ms
10 dnvr-kscy.abilene.ucaid.edu (198.32.8.13) 40.823 ms 41.181 ms 41.076 ms
11 snva-dnvr.abilene.ucaid.edu (198.32.8.1) 65.436 ms 66.068 ms 65.569 ms
12 198.32.249.161 (198.32.249.161) 65.673 ms 65.771 ms 66.006 ms
13 BERK--SUNV.POS.calren2.net (198.32.249.13) 67.183 ms 67.131 ms 66.858 ms
14 pos1-0.inr-000-eva.Berkeley.EDU (128.32.0.89) 67.192 ms 66.749 ms 67.720
ms
15 vlan198.inr-201-eva.Berkeley.EDU (128.32.0.194) 67.373 ms 67.067 ms 67.82
1 ms
16 fast8-0-0.inr-210-cory.Berkeley.EDU (128.32.255.122) 67.634 ms 68.735 ms
68.413 ms
17 GE.cory-gw.EECS.Berkeley.EDU (169.229.1.46) 67.575 ms 68.222 ms 67.772 ms
18 gig8-1.snr1.CS.Berkeley.EDU (169.229.3.66) 67.454 ms 67.988 ms 67.177 ms
19
now.CS.Berkeley.EDU (128.32.44.96)
Linux Networking
67.892 ms *
67.818 ms
24
Lal Paul